Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
307q~8
-- 1
The present invention relates to a process for
reducing environmental influences on powder coating of
a workpiece, in which coating process the workpiece is
coated at least in part in a coating zone from a powder
feeder with air-conveyed powder; to a powder coating
facility; and to application of the process and,
respectively, use of the powder coating facility.
In the powder coating of workpieces, especially
coating of the latter with synthetic resin powders, such
as in the synthetic resin powder coating of can bodies,
inter alia their longitudinal weld seam, the problem arises
basically that environmental factors, such as atmospheric
humidity, degree of contamination, affect the properties
of the film formed on the workpiece by repeated melting
of the applied powder Such coating procedures are
frequently utilized in line in the immediate vicinity with
: other processing stations, such as with w~lding units
for the longitudinal seams of can bodies as the workpieces,
. as a consequence, the ambient air is contaminated with
oil vapors and other vaporization products of the
welding stepO
--` 1 307~28
-- 2 --
The invention has the objective of at least
reducing effects of the environment on the result of the
coating process; this objective is achieved in a process
of the above kind in accordance with the invention by
conditioning the air and at least extensively preventing
pene~ration of ambient air at least to the coating zone
for the workpiece.
On account of the feature that the air by means
of which the powder is conveyed to the powder feeder is
conditioned, i.e. its atmospheric humidity is maintained
at a predetermined value, and that air is used, the
residual contamination degree of which influences the
powder coating only to a negligible extent, in conjunc-
tion with the feature that air from the immediate surround-
ings is precluded from penetrating to the coating zone,the objective is attained that the coating procedure
can take place under predetermined, controlled environmental
parameters. In this connection, first priority must be
given to the essential feature that such measures are to
be taken at the coating zone proper, i.e. at the location
where the powder is delivered and applied to the workpiece.
Additionally, an environmentl controllable as described
above, is maintained with respect to the workpiece with
the powder application preferably for such a time period
until the powder coating to be produced can no longer be
impaired by fluctuating environmental influences.
-` 1 307~2~
-- 3 --
In conventional powder coating processes wherein
workpieces are coated in series one after the other,
the powder feeder being moved relatively to the workpiece
during the coating step, the additional suggestion is
advanced, for preventing penetration of ambient air, to
provide a chamber that is open at least on one side for
the relative movement between workpiece and powder
feeder, and to produce an air flow out of the chamber
opening into the suxroundings.
By providing such an air flow fxom the chamber
arranged around the coating zone, it is ensured that only
conditioned air, thus the powder conveying air, enters
the chamber.
It is furthermore known in powder coating pro-
cesses to return by suction any powder not applied to
the workpiece and/ox not remaining applied to the work-
piece, this sucked-back powder usually being recycled to
the powder feeder in a conveying cycle. The powder,
delivered in this arrangement in a closed cycle repeatedly
to the coating zone, which us~lly is in free communica-
tion with the immediate environment, becomes increasingly
soiled at the coating zone and also absorbs increasing
amounts of moisture. Even though the problem of growing
moisture in the powder can perhaps be controlled in a
powder processing unit at relatively high expense, it is
impossible in the aforementioned conveying cycle to keep
the repeatedly fed powder clean at reasonable expPnse.
''
:'' '
- 4 ~ 1 3 0 7 q 2~
Fbr this reason, quite special significance resides in
utilizing the process according to this invention in
a powder coating procedure wherein excess powder is
repeatedly dispensed in a conveying cycle along the above
lines. A powder reprocessing facility and/or stage,
otherwise required, thus becomes superfluous.
In a coating process wherein at least one
exhaust for air and powder not applied to the work~iece
and possibly, as explained above, returned in a conveying
cycle to the powder feeder, is provided, it is further-
more suggested that the air flow out of the chamber opening
is produced by feeding, per unit time, a larger quantity
of conditioned air to the chamber than the amount of air
exhausted therefrom. In this connection, the aforementioned
balance of conditioned air introduced into the chamber
and air removed from the chamber can also be influenced
in the aforementioned sense by generating the air flow
by conditioned air fed into the chamber in addition to
the conditioned conveying air.
If the aforementioned outward flow from the
chamber is produced exclusively with conditioned air by
designing the above-mentionedbalance per unit time cor-
respondingly large in favor of the conditioned air that
is introduced, then a relatively large quantity of
conditioned air is used up, entailing a corresponding
design of a climatizing stage and perhaps purification
stage for the aforementioned air. Also, it is to be
--~ 1 30792~
kept in mind that the amount of conditioned air conveyed
per unit time is not arbitrarily adjustable because this
amount directly affects the powder coating process, for
example via the delivery rate. For this reason, it is
S desirable in most cases to sepaxate setting parameters for
the coating step from setting parameters for the flow ac-
cording to this invention. To this end, conditioned air
without powder is introduced into the chamber in addition
to the aforementioned conveying air.
The feature of passing air through nozzles
furthermore in the region of the chamber opening, and in
such a case preferably unconditionad air, so that a flow of
conditioned air out of the opening of the chamber toward
the outside is produced in the chamber hy jet pump effect,
provides the result that, on the one hand, less conditioned
air needs to be utilized in that the pump jet forms
practically a barrier against the influx of ambient air
into the chamberO
In order to prevent excess powder from settling
on the chamber wall, it is furthermore proposed to
electrically charge the powder predominantly in one polarity,
the powder being electrostatically repelled by the chamber.
This is done preferably in case the powder coating step
is effected with electrostatic enhancement by producing
an electrostatic field in the zone of the workpiece,
charging the delivered powder, and driving the latter
by the force of the field against the workpiece. In this
.~ .
'I 3()'792g
-- 6
case, for example, a metallized inside wall of the
aforementioned chamber, designed insulated toward the outside
for protection against electric shock, is placed at the same
electric potential as an electrode in the coating zone, this
electrode generating, together with the workpiece placed at
corresponding electric potential, the electrostatic field for
applying the powder.
A powder coating facility according to this
invention, where environmental influences are mitigated,
comprises a conditioning chamber, at least one feed conduit
extended into the chamber and terminating in a coating zone
for powder conveyed by means of conditioned air, an air
conditioning device connected to the feed conduit as well as
likewise connected to conveying means for the conditioned air
with powder, at least one opening in the chamber for the
introduction of a workpiece to be coated, and means for
producing at the chamber opening an air flow oriented toward
the surroundings of the opening. The process of this
invention as well as the powder coating facility according to
this invention are suited, in particular, for the internal
coating of hollow items, in this connection also especially
for the seam coating of longitudinal weld seams in can bodies,
taking place customarily directly downstream of a welding
facility where the contaminations mentioned in the foregoing
are relatively pronounced. The aforementioned process and,
respectively, coating facility, however, can also be utilized
for the all-around internal coatings of hollow articles.
` 7 _ 1 307928
The invention will be described in greater detail
below with reference to the drawings wherein:
Figure 1 shows schematically a first embodi-
ment of a powder coating facil-ity according to this
lnvention, operating in accordance with a process of this
nventlon,
Figure 2 shows a second embodiment of the powder
coating facility operating according to a process of this
invention, again in a schematic view,
Figure 3 is a schematic view of a chamber in
a powder coating facility according to this invention,
Figure 4 shows a preferred embodiment of a powder
coating facility for the internal coating of longitudinal
weld seams of metal can bodies, directly downstream of a
lS welding facility for the longitudinal weld seam.
'`; ' ~ .
,
,
- 8 _ 1 3 (~ 7 S 2 8
According to Figure 1, a powder coating facility
comprises an air conditioning unit 1 wherein ambient air
is conditioned, for example maintained at a predetermined
! atmospheric humidity and/or purified of dust, oil particles,
, 5 etc. The ambient air LK conditioned in unit 1 is fed by
way of a conveying means 3, such as a fan, to a mixing
' uni~ 5, for example with a diffuser as illustrated
.~ schematically, where fresh powder PF fed from a powder
; storage tank 7 is mixed, optionally by way of a volume
control device 9, with conditioned air LK fed thereto.
On the outlet side of the mixing unit 5, fresh powder PF
is conveyed with the conditioned air LK via a feed
conduit 11 to a delivery means 13 in a coating zone 15 and
dispensed at that location. A workpiece 17 to be coated,
such as a can body to be coated on the inside or outside,
the longitudinal weld seam of which is to be powder coated,
is introduced into the coating zone 15 by means of a
schematically illustrated conveyor 19 and, after termina-
~ tion of the coating step, either returned again along the same
; 20 route, as indicated by double arrow A, or further conveyed
out of the coating zone 15 in the same direction, in case
of a procedure continuous in one direction, as shown by
arrow B.
In order to reduce, in accordance with this inven-
tion, effects of the environment U on the coating of the
workpiece 17 produced at the coating zone 15, such as
fluctuations of relative atmospheric humidity, contaminants
` ~
- 9 - 1 3 0 7 ~ 2~
in the air, in this connection particularly from
processing stations for the worlcpiece 17 arranged
upstream or downstream thereof, the penetration of air
from the surroundings U is maximally prevented, at least
at the coating zone 15.
This is achieved by providing, as shown in
Figure 1, a conditioning chamber 21 which encompasses
especially the coating zone 15 and optionally additionally
a predetermined sec~ion within which the workpiece 17
is traveling after the freshly applied coating. This
additional route optionally likewise enclosed by the con-
ditioning chamber 21 can also comprise further systems,
such as a first heating stage by means of which the applied
synthetic resin powder layer on the workpiece 17 is heated
up to form a continuous film or film strip.
The conditioning chamber 21 exhibits, in case
of pendulating feed according to double arrow A, an
opening 23 through which the workpiece 17 is fed to the
coating zone 15 and ayain removed therefrom. In case the
workpiece 17, in continuous operation, is transported in
one direction according to arrow B to the coating zone 15
and away therefrom, the conditioning chamber 21, as shown
in dashed lines, has a second opening 23 through which
then the coating workpiece 17 can be further transported
by means of the conveyor 19.
o - I397~2~
~ Provision of the conditioning chamber Zl has
the result that, neglecting the amount of powder ~PF
fed per unit time, based on the amount of conditioned
conveying air ~ K delivered from the outlet 13 per unit
time, a flow S of conditioned a:ir LK out of one or both
provided openings 23 is maintained, preventing uncondi-
tioned air that is contaminated and/or has undesirable,
uncontrollable atmospheric humidity f~om the surroundings
U, from passing into the coating zone 15.
However, in this connection, it is to be kept
in mind that the amount of conditioned conveying air
ed to the chamber 21 per unit time via the feed con-
duit 11 is to be set predominantly based on the requirements
of the coating process per se at the coating zone 15.
Therefore, if this amount of conditioned conveying air
introduced into the cha~ber.21.:.with:a view toward a desired
coating step is not sufficient for ensuring adequate flow S
from one or both openings 23, then additionally condi-
tioning air LK is fed to the conditioning chamber 21 from
the conveying means 3 and from the conditioning facility 1;
consequently, the flow S can then be adjusted to an adequate
value, independently of the coating processO
Figure 2 shows schematically a coating facility
according to this invention, basically as illustrated in
Figure 1. Identical parts and/or functional blocks bear
the same reference numerals as in Figure 1.
1 30792~
-- 11 --
:,'
In powder coating facilities of the type-shown
schematically in Figure 1, it is conventional to return,
by suction, along the lines of recovery, any synthetic resin
powder that has not adhered to the workpiece 17 and/or
powder exiting from the discharge means 13 when no work-
piece 17 at all is present in the coating zone 15. For
this purpose, as illustrated in Figure 2, a return exhaust 25
is arranged in the zone of the delivery 13, downstream and/or
upstream, connected to a corresponding suction unit 27,
such as a pump. By means of this return exhaust 25, powder
that has not adhered to the workpiece 17 is returned by
suction with the aid of conditioned air LK.
Since in many cases the powder/air stream from the
discharge means 13 is not interrupted at the time the
coating zone 15 does not contain a workpiece 17, i.e. until
the subsequent workpiece 17 arrives, an additional return
exhaust 29 is provided, with an exhaust hood 31, likewise
in cormmunication with the return exhaust unit 27.
The ~owder from the return exhausts 25 and 29,
sucked back with conditioned air, is again fed into the
feed conduit 11 in order to be reissued, in a closed cycle,
at the outlet 13 against the workpiece 17. The mixture of
sucked-back, no longer fresh powder P with the fresh
powder PF from the powder tank 7 is effected, for example,
by a dosing rneans and/or a mixer 33.
. ~ ..,,,, ~,.
, . .. .
- 12 1 3 ~79 28
-
;
! Without provision of the features according to
this invention, precisely the operation of such a powder
cycle, wherein powder already applied once or several
times is mixed with fresh powder and reapplied, is prone
to incur an increasingly impaired coating action, for the
powder, applied again and again, absorbs moisture and dirt,
such as oil vapors, etcO, of processing stages arranged
upstream or downstream thereof, from the surrounding air,
with a practically integral characteristic over time.
This problem is eliminated by providing the
conditioning chamber 21 of this invention, and there is no
need to include an expensive powder reprocessing stage for
dehumidifying and/or purifying the reapplied powder that
has already been utilized once or repeatedly.
In order to produce an outward flow S in this case
at one or both openings 23, the balance of conditioned
air mLKin fed per unit time to the chamber 21 via the feed
conduit 11 and of the amount of air mLK~ut returned by
suction per unit time by means of the return exhausts 25
and 29 is chosen to be positive in favor of the amount of
air introduced into the chamber 21. To avoid having to
optimize the quantitative parameters determining the actual
coating step, the amount delivered from conduit 11 and
the amount returned by suction, especially at 25, in
- 25 deference to additional requirements, namely production of
an adequate flow S, it is here also suggested to provide,
starting at the conveying means 3, additionally a
~ 13 - 1 3n792~ '
conditioning air conduit 35, with the aid of which
additional conditioned air LK, along the lines of a
positive effect on the aforementioned balance, is intro-
duced into the chamber 21. In this way, the objective is
achieved that the powder, on the whole freely exposed in
the coating zone 15, cannot be contaminated by the environ-
ment U, thus eliminating the need for expensive processing
steps, as mentioned above. The powder cycle, othexwise open
at the coating zone 15, is accordingly closed with respect
to the environment U by meansof the chamber 21 also at that
location.
In the embodiments according to Figures 1 and 2,
the flow S from the provided openings 23 of the chamber 21
is generated exclusively by conditioned air; as a conse~uence,
a relatively high-power conditioning unit 1 must be included.
Figure 3 illustrates schematically a further
version of producing the flow S, usable in connection with
both arrangements according to Figures 1 and 2. Here again,
the same reference symbols are utilized for identical parts.
In Figure 3, all of the elements of the facility accord-
ing to Figures 1 and 2 unnecessary for explaining the
procedure for producing the flow S according to this inven-
tion have been omitted.
A no~zle array 37 is provided in the region of
the opening 23, for example a slotted nozzle arrangement
along the periphery of said opening 23, or a plurality of
individual nozzles jointly supplied through a duct 39.
,
~ ;.~,,
f,~
'
- 14 - 1 3 07 9 2 ~
A jet 43 exits as a free jet from the nozzle or nozzles 41.
Due to the fact that the jet 43 is oriented at least in
one component S' transversely to the opening 23,
air is pulled from the interior of chamber 21 by the
formation of the jet and is conveyed into the surroundings:
Thereby, the desired flow S out of the opening 23 is
produced. The jet ~3 from the nozzle arrangement 37 can now
be generated with ambient air LU by means of a conveying
unit 45; as a result, the conveyor 45 can be located in
the immediate vicinity of chamber 21, only short conduits 47
are required, and less conditioned air L~ is used up for
the flow S. The jet 43, in accordance with the jet pump
principle, has a suctioning effect on the interior of
chamber 21.
Figure 4 shows schematically a preferred embodi-
ment of a coating facility of this invention, operating
pursuant to the process of the invention, designed for the
internal coating of weld seams of metal cans. The feed
conduit 11 and the return exhaust 25 are arranged in a
projecting working arm 49 which, in Figure 4, on the left-
hand side, is mounted following a welding station for the
above-mentioned longitudinal weld seam and projects from
there toward the right. Can bodies 51 welded together
along their longitudinal edges at the welding station
(not shown) are moved by means of a conveyor, not il-
lustrated herein, in the direction of arrow B via the
arm 49, through the arrangement at a spacing with respect
~ f
- 15 - 1 3 ~7 ~ ~
to the orifices of the feed conduit 11 and, respectively,
of the return exhaust 25. During this step, the weld seam
zone 53 of the can bodies 51 is coated by the powder
delivered from conduit 11 by means of conditioned air Lx.
Excess powder, and power dropping off the can body 51 is
sucked back, as mentioned above, through the return
exhaust 25, and the powder fed in the upward direction
between the can bodies 51 following in rapid succession
is exhausted by the return exhaust 29.
10 The conditioning chamber 21 encompasses, in
particular, the coating zone 15 and optionally also part
of heating units lying downstream thereof, not shown in
Figure 4, with the aid of which the applied powder coating
is fused.
The chamber 21 is supplied with additional con-
ditioned air LK by means of the conditioning air con
duit 35, in such a way that according to this invention
a flow S is generated out of the openings 23 of the
conditioning chamber 21.
In order to enhance the powder application to
the can bodies 53, an electrode 55 is located in the zone
of the discharge 13; this electrode is placed at a high
electrostatic potential V with respect to ground, whereas
the can bodies 51 are connected to ground, for example
by way of the conveyor (not shown). Thereby, a high
electrostatic field is generated in the coating zone 13
oriented so that powder particles, charged primarily ~th
1 301~28 - 16 -
one polarity, either by friction in the feed conduit 11
and/or by the effect of the electrode 55, are driven by the
force of the field against the can bodies and retained
thereat. To prevent powder that may not hav~ been returned
through the exhaust from settling in the interior of the
conditioning chamber 21, the latter and especially its
inner wall region is likewise placed at an electrostatic
potential, such as the electrostatic potential V of the
electrode 55, whereby a field E repelling the charged powder
particles is generated in the wall zone of the conditioning
chamber 21. If the inner wall of the chamber 21 is
placed at a high electrostatic potential, then the outer
wall of chamber 21 is furthermore equipped with an insulating
jacket, as illustrated at 57, to provide protection against
electric shock. Further, as shown at 59, the conduit 35
is in this case electrically decoupled from the chamber 21,
and likewise additional, outwardly extending elements and
parts in contact therewith.
The proposed invention, the process, or the
coating facility achieve the objective that, without
expensive measures, environmental influences cannot affect
the quality of the powder coating and a uniformly controlled
coating can be effected.
